Center pivot irrigation systems are used extensively in agriculture. The center pivot irrigation system consists of a series of sprinklers on a movable pipeline. At one end of the pipeline is an end gun sprinkler. Its purpose is to extend the range of operation of the sprinkler system beyond the length of the pipeline.
The end gun normally applies three to twenty times as much water as the other sprinklers that are arranged along the elongated sprinkler pipeline. The end gun sprinkles at a different angle than the other sprinklers. The end gun sprinkler mechanism is similar to an impulse lawn sprinkler, only on a larger scale.
The end gun includes an overcenter device that hits a stop at one end of an end gun path of travel to reverse end gun travel direction. After travelling the path, the overcenter device hits a stop at the other end of a desired arc or end gun path of travel where the end gun is reset to travel in the reverse direction. The end gun is moved across its path of travel by the force of a water stream directed against an impulse weight and vane on the gun.
A center pivot irrigation system cannot operate without water; once the system is pressurized it cannot be stopped until the water pressure is removed. Adjustment of the center pivot irrigation system end gun is critical for correct crop watering, and yet it is difficult to perform end gun adjustment correctly.
To adjust the end gun, one has to shut the system down, travel to the end gun, put up a ladder (which may be fifteen feet in the air; and where the ground is normally wet and soft), and try to adjust the end gun stops. Such a procedure is both time consuming and subject to repetitive trial and error adjustment until a correct setting is obtained.
After an initial adjustment is made, the pivot irrigation system is turned back on and the adjustment must be checked for accuracy. This process is repeated over and over again until the end gun spray pattern is correct. Much time and effort is wasted on this procedure. Consequently, end gun adjustment is not performed as often or as accurately as it should be.
In addition to the difficulty of initially adjusting the end gun in a center pivot sprinkler system, there is the problem of wind effect on end gun sprinkler spray pattern. When the system sprinkler is operating during windy conditions, there is an area of over watering on the upwind side of the end gun; there is an area of under watering on the downwind side of the gun. The difficulty of adjusting the end gun when conditions are ideal (no wind) makes it wholly impractical to try to compensate for wind effect on end gun spray patterns.
Uneven crop watering due to wind effect on the end gun spray patterns is a waste. It is a waste of energy to pump the water, it is a waste of the water, and it is a waste of time. Farming is a business activity that produces a narrow margin of profit. Any inefficiency in farm operation that reduces that narrow profit can mean the difference between a profit or a loss on a year's crops. Inefficient watering--in addition to raising the cost of producing a crop--decreases the yield per acre in a given crop. Lower yields mean lower returns and losses or reduced profits.
Various crude solutions to the problem of end gun adjustment have been suggested. Examples of such proposed solutions are the Coash U.S. Pat. No. 4,128,205 issued Dec. 5, 1978 and the Sherman U.S. Pat. No. 2,988,287 issued June 13, 1961. These prior attempts to solve the end gun adjustment and wind effect problems have relied on mechanical control of end gun spray intensity and inclusion of auxiliary nozzles. Although the problems inherent in center pivot sprinkler irrigation systems have been recognized and attempts have been made to solve the problems, there has as yet been no satisfactory solution to the problem of end gun adjustment and wind compensation.